One punch man meets Majin Buu
by JuleNkata
Summary: Majin Buu seeks to kill Goku and Vegeta, but he runs on a different foe instead. How will things work out?


Back with a crossover story of OPM x DBZ.

Hope you like it!  
short intros before anything else.

DBZ timeline: when Kid Buu first appeared in his battle against Goku and Vegeta.  
OPM timeline: some random time during Garou arc.

* * *

DRAGONBALL Z INTRO:  
Gohan, Picollo, Trunks and Goten were finally saved by Goku and Vegeta inside the body of Super Buu. The process was long and hard but they barely made it out. Everything was meant to be over at that moment, at least for them.

"UHAAAAHOAAAAAAAAAAAAAAAAAAAAAAAA!" Majinbuu screams, starts to light up and release steams from his head.

Goku and Vegeta prioritized their 4 comrades before anything else. They took them to a safe place before checking on Majinbuu again.

"What the fuck is happening to him?" Vegeta asked.  
"I dont know! But I sense an insane amount of power and evil from him!" Goku answered.

"Shit! Is he done!?"

"UAAGHHHHH!"  
"HAAAAAAAAAAAAAAA!"

Goku and Vegeta went in their super saiyan 2 forms in response to Buu's unfathomable power building up.

"Shit! You and your stupid ideas of saving the kids! We could just revive them with the dragon balls!"  
"Stop whining and just focus! We can still fight unfused!"

 **'I-its over! Gokuuuuuuu!'** Kaio from the other world spoke to them via telepathy and told them Buu was transforming to his original, most evil and dangerous form.

Kid buu was finally revived in the middle of their conversation releasing a particularly small light of ki blast in the middle of Goku and Vegeta.

". . . . He he hi hi he, KILL YOU TWO!"

 _ **"!"  
"That small fragment of Ki can destroy the planet!" **_Goku thought to himself ** _._**

"Darn it! It's not supposed to hit us but the planet itself!"  
"FINAL BURST CANNON!" Vegeta desperately charged as much Ki as possible and deflected Buu's energy blast with his, sending him and Goku flying by the impact.

"AAAHHH!"  
A huge explosion echoed around the world.

"We can't do it anymore! This world is doomed! The little shit is charging a bigger one!"  
"We need to run! Take Gohan and the others with us! We can just bring back the world with the dragon balls!" Goku exclaimed.

. . . . . . .

. . . . . . . . .

Goku and Vegeta couldn't do anything to save the planet. They barely made it out and Earth was destroyed.

Buu regenerated in the vacuum of space. Eager to battle Goku and Vegeta again, he teleported from planet to planet, Blowing it up as soon as he feels the absence of the Goku and Vegeta's Ki.

Until he teleported in the middle of _**A-City**_ , in Saitama's planet.

* * *

ONE PUNCH MAN INTRO:

 _Inside Saitama's house in Z-City_ _  
_

 ***Knock Knock***

"Oh? What brings you again, Fubuki?"

"Are you kidding me? Since you are part of the Blizzard Group, I need to visit you once in a while." Fubuki answered.

"Since when did I become a part of your group again?" Saitama sighed.

"She just wants to see you, Saitama." King butted in.

"S-shut up king! What are you doing here anyway? An S-Class hero?"

"I could ask you the same thing B class rank 1."

"Y-you!"

"For God's sake when are you gonna let me play King? I'm waiting." Saitama seemed oblivious.

King and Fubuki had some minor banters while Genos prepared the food Fubuki brought for everyone.  
It was just another peaceful day in Z-City, or is it?

 _BREAKING NEWS! A Monster was spotted in the northeastern vicinity of A-City. The disaster level is... God!? This has never happened before! We need the best heroes to deal with it!_  


"Hmph. The hero association is right in A-City, we don't need to worry about that lone monster, he made a mistake." Fubuki assured.

Saitama had an anxious look in his face, he stood up. He sensed a power far greater than anything he had faced before.

"Sensei, are you going?" Genos asked him.

"Hmm? I have to go. You guys stay here." Saitama had a grin in his face.  
"Save me a bit of those Tonkatsu and Sushi alright?" he followed up.

"Fubuki will save some for sure, not sure with myself." King answered.

"Shut up king!"

Saitama changed to his hero outfit and started running towards A-City, he felt as if the entity was waiting for him.

* * *

As soon as Kid buu teleported in A-City, he was about to blow it up when he felt the presence of the powerful S-class heroes. He calmed down and started walking in search for them. He momentarily forgot about Goku and Vegeta.

 _"hi hi hi he he me buu, kill you! kill you!"_

 _"Hey, are you a hero? That costume looks creative and good, but overall you look funny."_ Suddenly, a random guy approached him and gave neither a praise or insult.

Buu had a disgusted look on his face as he released a powerful energy blast right at the guy's face, completely atomizing him along with the buildings around.

"HEEEELPPPPPP! AHHHH!"  
"IT'S A MONSTER!"

"MOMMY! WAHHHH!" Cries can be heard everywhere.

People started to panic and run. Buu didn't waste any time and killed them with Ki blasts. He flew a hundred meters to the sky, A-City was huge. He didn't plan to destroy the entirety of the city so he made a number of small energy blasts which killed thousands of people and made huge, deep craters on the city.

"HA HA HA HA HA HE HE HE!" Buu had a hysterical laugh. He seemed to enjoy what he was doing.

"OOOOOOOOFFF!" Until an unknown energy sent him flying several hundred meters.

"Who the hell do you think you are?" It was the voice was Tatsumaki, the strongest esper the hero association has to offer.

At the same time, Many S-class heroes appeared out of nowhere and attacked Buu without any restraint.

"Take this you piece of shit!" The anger was very clear in Tanktop master's voice.

Pri-pri prisoner, Atomic samurai, Metal bat, Child emperor and Zombieman joined the attack, there was a huge explosion and the land fell apart. The anger was very clear in the heroes' faces. A-city never had casualties as great as this.

A-class heroes came at the same time, namely Sweet mask, Stinger, Blue fire, lightning max, golden ball and heavy tank.

 **"!?"**

"Don't tell me I missed the party?! This fucker killed almost half the population of A-City!" Sweet mask was very frustrated.

"You guys don't need to move. This is a job for us S-class heroes. And we did it." Child emperor answered him.

"All those beautiful men killed." Pri-pri prisoner had tears in his eyes.

"Show me his corpse! I will rip him apart until nothing is left!" Sweet mask insisted.

Everyone had a sad look on their face. Tatsumaki felt anxious, she could still feel the presence of the powerful entity they just killed, or did they?

"IF YOU DID THIS MUCH DAMAGE TO A-CITY THEN THAT ATTACK WON'T KILL YOU! SHOW UP AND FIGHT ME YOU COWARD!"

Sweet mask kept cursing on Buu as everyone saw something was forming behind him, Tatsumaki quickly realized it was Buu regenerating from their attacks.

"Hey! Behind you!"

Sweet mask had no time to react other than turn around and see Kid Buu's grin, and then everything turned black for him, he was dead in an instant.

Sweet mask immediately fell down lifeless as Buu clapped his hands on his head, crushing his skull. He then proceeded to the other A-Class heroes and killed them. The S-class heroes retaliated and there were huge explosions everywhere. Everyone was going all out.

MEANWHILE...

Saitama was close to where Buu was fighting and sensed Many heroes and people dead, the city was almost completely obliterated. It was the first time he felt an intense emotion in him. The feeling of sadness and anger. He had a vexed look in his face, never seen before by anyone.

 _ ***pant* *pant* *pant***_  
 _ ***cough* *gasp***_

Tatsumaki was all that's left. She was crying and trembling, she realized she was weak and couldn't do anything to save her fellow heroes or even kill the monster in front of her. She was filled with fear and disappointment.

 ***sob*** "I. . . Will avenge . . them. I'm the only one who can. . do it." ***cough* *sob***

"Buu better in magic! Turn you candy! hi hi hi hi!" Buu spurted his last insults before pointing his antenna on her. Tatsumaki closed her teary eyes and just waited for her certain death.

When suddenly, Buu felt something heavy. He was unconscious for a second and realized half of his face was gone and something sent him flying.

He braced himself mid-air and looked sharply at where Tatsumaki is. His eyes crossed and widened the moment he saw someone wearing a cape and a yellow outfit, he was bald.

The thought of him getting hit by the funny looking guy irritated him. He charged towards them going for the kill, sending a huge ki blast on Tatsumaki's way and attacking Saitama himself, only to get punched and sent flying miles again.

"UOAHHHHH!"

Saitama quickly rushed towards Tatsumaki carrying her off the path of the Ki blast. The buildings around were completely decimated.

". . . You okay?"

"Y-you. . again? What can a B-class hero do here?" Tatsumaki replied.

"Hm? You needed help so I came." Saitama answered.

"I dont need your help egghead! I could have finished him off myself! And let go of me pervert!" ***cough* *cough***

"Hmm? Who the hell you're calling a pervert?" Saitama dropped her to the ground.

"Ouch! Be more gentle you stupid baldy!"

Suddenly, there was a huge earthquake. The two quickly realized it was Buu again, preparing to attack them.

"Fubuki is on her way here. Get some rest and I guess I'll protect you for now." Saitama turned his back as he encouraged her.

". . . . Protect me?" Tatsumaki looked up to him agitated. She never expected those words from him. She was starting to admire and respect Saitama at the same time.

"How strong is he?" Saitama asked.

"B-be careful! That opponent is beyond words!"

"Hm?" Saitama started walking off.

"Hey! Im telling you be really careful!" ***cough* *cough***

Buu suddenly teleported in front of saitama and landed a fist on his face. The landscape Saitama was stepping on collapsed but he didn't move an inch. Buu opened his palms and charged up a point blank ki blast in Saitama's face. The huge explosion caused a massive shockwave that shattered nearby buildings.

"B-Baldy!" Tatsumaki screamed.

"Hi hi hi hi hi! he he!" Buu was laughing.

The smoke and dust cleared up, Buu saw Saitama unfazed and only his cape was a little burned. Saitama immediately grabbed Buu's antenna, smacked him on the ground twice and threw him far away from A-City, where they can fight freely.

"Well, guess I'm off?" Saitama looked at Tatsumaki one last time before leaving.

"B-be careful!" ***COUGH* *COUGH***

. . . . . . . . . .

He skyrocketed towards where he threw Kid Buu. He was eager to fight something as powerful as Buu.  
Saitama landed on the ground with a huge impact. He saw Buu waiting for him, he was dancing like a rubber, as if to say "Im gonna enjoy killing you!"

"Don't disappoint me now." The hero had a smirk in his face.

"Buu, kill you! he he he!" Buu charged towards Saitama to attack.

Buu moved so fast he was literally disappearing, he seemed to teleport everywhere on Saitama's vision. On the other hand, Saitama stands idle as if waiting for an attack to land.

Buu landed a clean hit on Saitama's gut which sent him flying through several mountains, he followed up with a Ki blast and charged Saitama's way again.

Buu's vision lightened up, he realized his Ki blast was deflected back towards him. He quickly dodged it and saw Saitama over him, doing a forceful chop on his head.

"OAHHHHH!" Buu screamed. The impact of Saitama's chop burried Buu and made huge cracks on the ground.

Buu quickly retaliated by grabbing Saitama's legs from the ground burying him as well. There was a huge earthquake and the ground was splittling everywhere. They were exchanging blows underground.

 _ **'This guy is really good huh?'**_ Saitama thought to himself.

Buu landed an uppercut on Saitama and added a barrage of Ki blasts, there was a huge explosion underground and the hero was sent flying to the surface. Buu teleported right behind him mid air and returned a chop on Saitama's head, burrying his face on the ground.

Buu stopped his attack and laughed at Saitama.

"AHAHAHA! Buu hit your head too! HAHAHA!"

Saitama stood up and was surprisingly unharmed by everything Buu threw at him.

"Hmm? I wonder if its ok for me to kick an immature opponent's ass?"

"HE HA HA HA HA!" Buu kept laughing.

"Either way, you already did more than enough to piss me off." Saitama had a blank, yet annoyed look in his face.

Saitama blitzed and landed a quick, solid punch on Buu's gut. The impact was so strong the shockwave disintegrated nearby mountains. Buu was shattered to pieces but quickly regenerated on the spot, he started to exchange blows with Saitama.

"Buu kill you! Buu kill you!"

"..." Saitama had a blank expression in his face.

"Buu kill you!"

 _ **'Hmm. So he can regenerate, just like that Boros huh?'**_ Saitama thought to himself.  
"..."

The exchange of blows was fairly equal, Buu lands several hits but Saitama is completely unharmed, Saitama lands several hits and Buu quickly regenerates and seems unharmed as well. Until Buu heard the hero mumbing something to himself.

"Super moves serious series..."

"Serious . . . "

"Serious . . "

 _ **!?**_

Buu sensed the killing intent of Saitama's incoming attack, he quickly leaped away from him. It was the first time he felt fear.

"Ohh? Why did you back off?" Saitama calmed down with a disappointed look in his face.

"Grrrrr. Buu KILL YOU! KILL YOUUUU!" Buu started to release steams from his head. He was very pissed by the fact he got scared for a moment. He charged his Ki and quickly flew towards Saitama fully bloodlusted. He blitzed the bald hero and landed thousands of hits and Ki blasts everywhere in his body.

"GAAAAAHHHHH BUU KILL YOU AND THIS PLANET!"

Saitama coudn't react, he took everything Buu was throwing at him.  
He was pummeled everywhere. Their battlefield extended thousands of miles, forests were burning, everything turned to a wasteland, the mountain ranges fell apart, there were huge craters everywhere, and the sky turned black.

". . . . . . ."

Even after everything Buu did, Saitama seemed unharmed even though his body was covered in scratches. Not even a single trace of exhaustion was visible in his face, Buu was angered even more.

"GRRRR..."

"Hmm? Why did you stop? My turn then." Saitama clenched his fist and threw a punch to the angry Kid Buu.

Buu barely dodged the attack. He was hit on his shoulder and his arm was shattered. He immediately regenerated but looked like he was struggling regenerating at this point, his hand was missing a finger.

"BUU TURN YOU CANDY! BUU EAT YOU!" Buu pointed his antenna on Saitama and tried to turn him into candy. There was a blinding light.

. . . .

"Ooooh.."

"Aababababababa. What the hell did you just do? That felt funny."

But it was useless. Saitama was unfazed. Buu got pissed off even more and started shouting again.

"HOOAAAAAAAAAA-!"

Saitama quickly followed up with a punch to his gut. Buu was sent flying.

"Nobody got time to wait for your wailing. Come at me with your fullest already will you?"

 _ ***HUFF* *HUFF* *HUFF***_

 _ **"HROAHAHAAHGHHHHHHHHHHH!"  
"AHAHAHA!"  
**_

 _ **"AHAHAHAHAHA!"**_

 _ **"..."**_

 **"AHA HA HA HA AHA! DIEEE!"**

"Hmm?" The hero suddenly felt something funny. he thought his knee was just itching."

"..."

"..." Saitama had a smug look on his face.

"... Hey.."

". . . Feels slimy."

". . . HUH!? THE FUCK IS THIS SHIT!?" Saitama exclaimed.

"AHAHAHA! Buu beat you! HAHAHA!" Buu laughed at the clueless hero.

"Wait a second. . This is... WHAT THE FUCK!?" Saitama started sweating and had a disgusted, funny look on his face, he squinted his eyes.

* * *

/A FLASHBACK RINGS INSIDE THE BALDY'S HEAD/  
 _Saitama recalled his high school classmate telling stories when he would watch nudes and his favorite category was tentacles. Aapparently this is what Saitama remembered as he is being swallowed by this "slimy" thing he calls._

* * *

"Yo. I'm a man. I swear to god if you are trying to impregnate me with this mucky booger I'm gonna smack your head inside out."

"AHAHAHAHAHA HAHA!" Buu ignored him.

". . ."

". . ." Saitama smirked.

". . . OK." Saitama answers himself.

Apparently, a part of Buu's arm Saitama shattered suddenly reformed around the hero and tries to absorb him. The hero was quickly swallowed by Buu's elastic proportion, and while Buu was celebrating with his hysterical laugh, he felt the pressure of something hitting him.

The thought of the hero resisting getting absorbed was predictable to Buu at this point, he had acknowledged Saitama as a very powerful adversary and he has willed himself to beat him more than anything else, more than Goku and Vegeta.

Saitama quickly broke through Buu's absorption, shattering the part of Buu's body that engulfed him as if they were made of bricks.

Buu teleports behind immediately and strangles Saitama with his antenna only to be grabbed and thrown in the sky. He quickly charged and sent a plethora of Ki blasts toward him, Saitama leaped toward him giving him a solid punch to the face.

"UGHAAAHHHHHHHHHH!" Buu's head was splattered and his body was sent flying upwards.

 _ **'Super moves serious series...'**_

 _ **'. . .'**_

Buu came back launching himself towards the hero enveloped with an insane amount of Ki he was literally burning up. He was going all out.

"GRRRRR. AHHHHHHH!"

 _ **'. . .Serious headbutt'**_

The two combatanats clashed in mid air. The impact was strong enough to cause turmoil on the other side of the planet and lava started gushing out everywhere.

 _ ***HUFF* *HUFF* *HUFF* *HUFF***_  
 _ ***PANT* *PANT***_

"Battle is over. You did well." Saitama gave Buu a smirk. _ **  
**_

 _ ***HUFF* *HUFF*** _ ". . KILL. . . YOU."

"You are really strong. I wonder if there are others stronger than you? The world is a really small place for us to battle huh?"

 _ ***PANT* *PANT***_

". .KILL. . . ." _ **  
**_

Saitama punched Buu one more time. Buu started shaking and his regeneration gradually slowed down, he was exhausted.

 _ ***PANT* *PANT* *HUFF***_

 _ ***PANT* *PANT***_

"You already lost. I'm going to finish you off right now." Saitama had a serious look on his face.

"KILL. . YOU. . NOW." Buu started charging up his last Ki. He didn't care about anything anymore, all he wanted was to defeat the man in front of him.

There was suddenly a huge earthquake as Buu started to power-up and go beyond his limits.  
 _ **  
**_"You don't need to worry, you are the stongest enemy I've faced." Saitama started talking with a calm face.

Buu's eyes darkened and his body bulked up. "KILL. . . YOU . . "

"Time for me to end your miserable life now, whoever you are." Saitama had a serious face.

 **"Super moves serious series. . . ."**

 **"Serious. . . Serious. . ."**

Buu started glowing and bulked up even more, He was ready for a final exchange against Saitama.

 **"DIEEEEE Ee E E!"** Buu blurted out his final words and gave everything in his last attack.

 **"SUPER SERIOUS. . . STRIKE."** Saitama's face was filled with anger on his attack. Perhaps it was the fact that even if he wins the battle, he won't be able to revive the casualties nor have the world recovered the way it was. He felt like it was a battle he won, and lost at the same time.

 _ **'Sorry. . . If I had come sooner. . . and if I had only. .'**_ Saitama started to talk to himself.

The collision of their attacks caused a blinding light and a huge explosion that can be heard halfway across the globe. the impact disintegrated everything thousands of miles away, the shockwave was enough to distort the point of impact. . .

The next thing shown was Saitama standing on the ground. Buu was completely atomized, Saitama won the battle. He turned back and looked at the dark sky.  
All he wanted at this time was to go back to A-City and check on everyone that survived.

 _ **'If I only had powers to bring everyone back, that would be nice.'**_ His face was filled with sadness as he started walking back towards A-City.

* * *

A-CITY:

Fubuki and the others were tending on the wounds of Tatsumaki while the other surviving medics from the neighboring cities also arrived helping the other survivors. The earth was completely devastated by Buu's attack. It was a nightmare that left a scar no one will ever heal and forget.

Saitama arrives at the scene and checks up their condition.

"You guys ok?" He asked.

"Sensei, had you not been here. Everyone would have.." Genos answered with a sad look on his face.

"Where's King and Bang?"

"There are some other S-class heroes that survived too but only a few. They are currently clearing up rubbles for possible survivors." Fubuki answered.

"Sensei, I'll go help them." Genos went on with the others.

". . ."

". . . Well, guess I'm sorry guys. If only i had come sooner-"

"OHHH YEAH YOU WERE SOOO LATE! Stupid jerk." Tatsumaki butted in before Saitama finished speaking..

 _ **'My god, this bitch.'**_ Saitama thought to himself.  
"Oh, your little sister is here."

"Shut up! I'm older than you and Fubuki! And I could have beaten that monster by myself if you never came! Stupid baldy!"

"SHUT UP YOU FUCKING MIDGET, do me a favor and get some rest so the world will stay quiet for a while." Saitama had a smug face.

"WHA-?. . . The fuck did you call me you BALDY!?"

"ENOUGH! THIS ISN'T THE TIME FOR THIS!" Fubuki shouted.

"And sis, weren't you asking for his name earlier?" Fubuki asked.

 ***COUGH* *COUGH*** "Oh yeah. Guess I should thank you for now. Baldy, what's your name."

"Oh? It's Saitama." Saitama answered.

"Okay Saitama. Thank you... For now. But one of these days I'll save your butt from a God level or Dragon level threat and we'll be even! You're still just a B-class nobody after all!"

Tatsumaki was reluctant, but deep inside she is thankful for Saitama's actions. Fubuki saw through it and just smiled.

A few hours after the battle, Goku arrived with Vegeta on A-City using instant transmission, there they saw Saitama with Fubuki, King, Tatsumaki, Genos and many other survivors.

"WAHH! NOT ALIENS AGAIN WHEN I'M NOT FULLY RECOVERED YET!" Tatsumaki shouted.

"Hmm? Who are they?" Saitama replied.

"Survivors?" Fubuki answered.

"They emit the same aura I felt on my last opponent." Saitama sighed.

. . . . . . .

"TH-THAT'S THE GUY!?" Vegeta seemed captivated.

"Might be. . Lets talk to them." Goku replied.

* * *

Goku and Vegeta acknowledged Saitama's strength and used the Dragonballs to revive his world, including all the killed heroes and inhabitants. Everyone lived normally again. Saitama's deeds reached the other side of the world and he was instantly promoted to S-Class rank 3.

...

With the addition of Tatsumaki, Goku and Vegeta started visiting his place during their free time. His place basically became more crowded than ever.

"Yo Baldy. You are still rank 3 and I am rank 2, so show some respect and honor everytime I visit your place!" Tatsumaki shouted.

"Umm. Sis." Fubuki answered.

"You guys know I could have defeated that monster but this egghead stole all the glory to himself! Hmph!"

"Tornado must be jealous of Fubuki coming here first. According to my analysis sensei." Genos followed up.

"HAH!? THE HECK DID YOU SAY?"

"OHOHOHOHO. To be young again." Bang teased.

"S-shut up Old man!"

"Yo, Saitama dude. Those 2 people calling themselves Saiyans said they'd be back tomorrow." King started talking.

"Actually **. .** " Saitama answered.

 **"How about you guys stop messing around my house and clean up all these junks you brought here? You already finished off all the Tonkatsus and sushi I have requested for fucks sake?. . GET OUT."** Saitama had a funny smug look in his face.

Apparently from this point onward, Saitama won't be living life the same anymore. He had many new companions. . Which annoyed him.

...

 _ **'. . .'**_

 _ **'. . . . . . . I guess I really am a hero after all?. . .'**_

The end.

* * *

Did you like it? I hope you do. Thanks for reading.

Story is open to sequels! Will gladly connect this story to other universes or another dbz character. But for now I will get some rest.  
Have a nice day.

:]d


End file.
